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論文

Density stratification breakup by a vertical jet; Experimental and numerical investigation on the effect of dynamic change of turbulent Schmidt number

安部 諭; Studer, E.*; 石垣 将宏; 柴本 泰照; 与能本 泰介

Nuclear Engineering and Design, 368, p.110785_1 - 110785_14, 2020/11

The hydrogen behavior in a nuclear containment vessel is one of the significant issues raised when discussing the potential of hydrogen combustion during a severe accident. Computational Fluid Dynamics (CFD) is a powerful tool for better understanding the turbulence transport behavior of a gas mixture, including hydrogen. Reynolds-averaged Navier-Stokes (RANS) is a practical-use approach for simulating the averaged gaseous behavior in a large and complicated geometry, such as a nuclear containment vessel; however, some improvements are required. We implemented the dynamic modeling for $$Sc_{t}$$ based on the previous studies into the OpenFOAM ver 2.3.1 package. The experimental data obtained by using a small scale test apparatus at Japan Atomic Energy Agency (JAEA) was used to validate the RANS methodology. Moreover, Large-Eddy Simulation (LES) was performed to phenomenologically discuss the interaction behavior. The comparison study indicated that the turbulence production ratio by shear stress and buoyancy force predicted by the RANS with the dynamic modeling for $$Sc_{t}$$ was a better agreement with the LES result, and the gradual decay of the turbulence fluctuation in the stratification was predicted accurately. The time transient of the helium molar fraction in the case with the dynamic modeling was very closed to the VIMES experimental data. The improvement on the RANS accuracy was produced by the accurate prediction of the turbulent mixing region, which was explained with the turbulent helium mass flux in the interaction region. Moreover, the parametric study on the jet velocity indicates the good performance of the RANS with the dynamic modeling for $$Sc_{t}$$ on the slower erosive process. This study concludes that the dynamic modeling for $$Sc_{t}$$ is a useful and practical approach to improve the prediction accuracy.

論文

Experimental investigation of density stratification behavior during outer surface cooling of a containment vessel with the CIGMA facility

石垣 将宏; 安部 諭; 柴本 泰照; 与能本 泰介

Nuclear Engineering and Design, 367, p.110790_1 - 110790_15, 2020/10

 被引用回数:0 パーセンタイル:100(Nuclear Science & Technology)

シビアアクシデント時の格納容器(CV)内の流体や構造物を冷却するための有効なアクシデントマネジメントとして、CVの外面冷却が期待されている。一方、以下のような可能性も考えられる。第一に、シビアアクシデント時に水-ジルコニウム反応により水素ガスが発生し、外表面冷却により水素を含む非凝縮性ガスが蓄積し、密度成層が形成される可能性がある。第二に、非凝縮性ガスの蓄積は熱伝達を低下させ、CVの冷却を阻害する可能性がある。これらの課題については、これまで多くの研究が行われてきた。しかし、外表面冷却によって生じる密度成層挙動や成層崩壊の条件に着目した体系的な検討は十分に行われていない。また、水素の蓄積による伝熱劣化を定量的に評価していない。そこで、実験設備CIGMA(Containment InteGral effects Measurement Apparatus)を構築し、CIGMA設備を用いて容器外面冷却時の格納容器熱流動挙動の実験的研究を行った。さらに、安定な密度成層が維持できる条件を考慮することで、自然対流が密度成層化挙動に与える影響を議論した。

論文

Unsteady natural convection in a cylindrical containment vessel (CIGMA) with external wall cooling; Numerical CFD simulation

Hamdani, A.; 安部 諭; 石垣 将宏; 柴本 泰照; 与能本 泰介

Energies (Internet), 13(14), p.3652_1 - 3652_22, 2020/07

 被引用回数:0

In the case of a severe accident, natural convection plays an important role in the atmosphere mixing of nuclear reactor containments. In this case, the natural convection might not in the steady-state condition. Hence, instead of steady-state simulation, the transient simulation should be performed to understand natural convection in the accident scenario within a nuclear reactor containment. The present study, therefore, was aimed at the transient 3-D numerical simulations of natural convection of air around a cylindrical containment with unsteady thermal boundary conditions (BCs) at the vessel wall. For this purpose, the experiment series was done in the CIGMA facility at Japan Atomic Energy Agency (JAEA). A 3-D model was simulated with OpenFOAM, applying the unsteady Reynolds-averaged Navier-Stokes equations (URANS) model. Different turbulence models were studied, such as the standard k-$$varepsilon$$, standard k-$$omega$$, k-$$omega$$ shear stress transport (SST), and low-Reynolds-k-$$varepsilon$$ Launder-Sharma. The results of the four turbulence models were compared versus the results of experimental data.

論文

Liquid film behavior and heat-transfer mechanism near the rewetting front in a single rod air-water system

和田 裕貴; Le, T. D.; 佐藤 聡; 柴本 泰照; 与能本 泰介

Journal of Nuclear Science and Technology, 57(1), p.100 - 113, 2020/01

 被引用回数:0 パーセンタイル:100(Nuclear Science & Technology)

The rewetting front propagation may occur when the fuel rod is cooled by the liquid film flow after it is dried out under accident conditions for BWR cores. Our previous study has revealed importance of precursory cooling, defined as a rapid cooling just before the rewetting, which has a significant effect on the propagation velocity. To understand the mechanism of the precursory cooling, we conducted heat transfer experiments using a single heater rod contained inside the transparent glass pipe to measure heat transfer behavior with simultaneous observation using a high-speed camera. The results showed characteristic effects of the wall temperature on the liquid film flow and liquid droplets formation at the rewetting front, i.e. sputtering. Even when the liquid film flows in rivulets under adiabatic condition, horizontally uniformed rewetting front was observed with increasing wall temperature due to enhanced flow resistance by sputtering. This sputtering effect was also confirmed from observations of the liquid film thickness, which increased with approaching the rewetting front. Heat transfer coefficients were predicted roughly well with a single-phase heat transfer correlation with entrance effects, suggesting the thinner thermal boundary layer downstream of the rewetting front may be one of the precursory cooling mechanisms.

論文

Study on dryout and rewetting during accidents including ATWS for the BWR at JAEA

佐藤 聡; 和田 裕貴; 柴本 泰照; 与能本 泰介

Nuclear Engineering and Design, 354, p.110164_1 - 110164_10, 2019/12

 被引用回数:2 パーセンタイル:31.52(Nuclear Science & Technology)

原子力機構ではBWRの沸騰後遷移熱伝達、過渡限界熱流束及びリウェットに関する一連の実験研究を行ってきた。これまでに、異常過渡条件をカバーする実験データベースが開発されており、またリウェット現象における先行冷却の重要性が認識されるようになった。本論文では、原子炉停止機能喪失事象、炉心熱伝達へのスペーサの効果、機構論的モデル開発のための現象の物理的理解に焦点を当て、これまでに得られた主な結果と共に、本研究のアプローチを提示した。

論文

CFD analysis of the CIGMA experiments on the heated JET injection into containment vessel with external surface cooling

Hamdani, A.; 安部 諭; 石垣 将宏; 柴本 泰照; 与能本 泰介

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.5463 - 5479, 2019/08

The present study introduces thermal mixing and stratification produced by heated air jet located at the bottom level of the containment vessel. The investigation was carried out experimentally and numerically in the large containment vessel called CIGMA (Containment InteGral effects Measurement Apparatus). The experiments were conducted with external surface cooling and various air jet inlet temperatures. The containment cooling was done by flooding the water on the external side of half-upper of a vessel. To identify their influence on the thermal mixing and stratification phenomena, the investigation focuses on mixing convection which occurred in the cooled region of a containment vessel. Temperature distribution and jet velocity were measured by thermocouple and Particle Image Velocimetry (PIV) respectively. Numerical simulation was performed using Computational Fluid Dynamics (CFD) code OpenFOAM to investigate the detail effects of external cooling on the fluid flow and thermal characteristics in the test vessel. CFD results showed a good agreement with experimental data on both temperature and velocity. Both temperature and velocity of hot air jet decayed rapidly downstream jet nozzle. Thermal stratification was observed by visualization of temperature contour maps over a cross-section in the containment vessel. Vigorous mixing was also noticed in the upper region of the containment vessel. Effect of external cooling on mixing and the thermal stratification were presented and discussed.

論文

Ultrasound measurement of upward liquid film flow in vertical pipe

和田 裕貴; 佐藤 聡; 柴本 泰照; 与能本 泰介; 佐川 淳*

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.4518 - 4531, 2019/08

原子力機構では、液膜のドライアウト・リウェットを液膜の有無を超音波液膜測定によって実現するための技術開発を実施している。原子力工学分野における従来研究では、使用する超音波の搬送周波数が5MHzと比較的低く、最小液膜厚さの限界値が実用的に0.1mm以上の厚い領域に限られていた。さらに、液膜厚さを評価する際の信号処理方法が生データと共に明確に示されておらず、それに伴う測定の不確かさにおける議論が充分ではない。そこで、本研究では15MHzの中心周波数を有する圧電素子と独自の駆動回路を用いた超音波液膜厚さ測定装置を開発した。本発表では、本装置における液膜測定の妥当性の検証結果、鉛直管内を流れる上昇環状液膜流を測定した結果及び管内測定に際する測定部の詳細設計について報告する。

論文

Experiment on density stratification behavior by containment venting using CIGMA Facility

石垣 将宏; 安部 諭; 柴本 泰照; 与能本 泰介

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.5927 - 5940, 2019/08

格納容器ベントシステムはシビアアクシデント時における格納容器の過圧を防止するための手段として適用される。ベント時に発生する現象の理解と最適な運用という観点から、格納容器ベント時の水素挙動に関する研究は十分ではない。そこで本研究では大型格納容器実験装置CIGMAを用いて格納容器ベントに関する基礎的な実験を実施した。特に、ベントによる水素輸送に対するベント流量及び初期ガス分布の影響について調査を行った。水素の代替ガスであるヘリウム,蒸気,空気を用いて、初期に容器内に成層を形成し、下部ベントラインからベントを実施した。ベントにより初期に容器下部に存在する蒸気・空気のみが排出され、ヘリウム成層が下方へと拡大していく挙動が観察された。この間、上部のヘリウム濃度は一定であった。最終的には容器内のガス濃度分布は均質化した。今回実施した実験条件では、ベントによる容器内のガスの顕著な混合は観察されなかった。また異なる初期濃度分布に対してもヘリウム成層の挙動に大きな差は見られなかった。

論文

Experimental investigation of decontamination factor dependence on aerosol concentration in pool scrubbing

孫 昊旻; 柴本 泰照; 岡垣 百合亜; 与能本 泰介

Science and Technology of Nuclear Installations, 2019, p.1743982_1 - 1743982_15, 2019/06

 被引用回数:0 パーセンタイル:100(Nuclear Science & Technology)

Because a pool scrubbing is important for reducing radioactive aerosols to the environment for a nuclear reactor in a severe accident situation, many researches have been performed. However, decontamination factor (DF) dependence on aerosol concentration was seldom considered. DF dependence in the pool scrubbing with 2.4 m water submergence was investigated by light scattering aerosol spectrometers. It was observed that DF increased monotonically as decreasing particle number concentration in a constant thermohydraulic condition. Two validation experiments were conducted to confirm the observed DF dependence. In addition, characteristics of the DF dependence in different water submergences were investigated experimentally. It was found the DF dependence became more significant in higher water submergence.

論文

Experiments on collapse of density stratification by outer surface cooling of containment vessel; CC-PL-12 and CC-PL-24 experiments at CIGMA

石垣 将宏; 安部 諭; 柴本 泰照; 与能本 泰介

Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 11 Pages, 2018/10

シビアアクシデント時における格納容器内熱水力挙動は安全上重要な課題の1つである。本研究では大型格納容器実験装置CIGMAを用いて、格納容器内の水素挙動および自然循環挙動に対する格納容器を外部から冷却した際の影響について検討した。本実験では2つの冷却手法を適用した実験を行った。1つは上部プールに蓄えた冷却水による冷却と上部プール・中段ジャケットへの流下液膜による冷却である。容器内に水素の模擬物質としてヘリウムを注入し、さらに蒸気と空気を注入し、容器上部にヘリウム成層を形成した際の成層挙動について計測を行った。冷却手法に応じて、異なる成層挙動が観測された。

論文

Influence of grating type obstacle on stratification breakup by a vertical jet

安部 諭; 石垣 将宏; 柴本 泰照; 与能本 泰介

Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 9 Pages, 2018/10

At Japan Atomic Energy Agency (JAEA), small scale experiment, named VIMES (VIsualization and MEasurement system on stratification behavior) experiment, has been performed since 2014. In this paper, we introduce the influence of grating type obstacle to the VIMES experiment. Two types of grating obstacle were constructed based on the aperture area ratio. The obstacles were placed at the intermediate position between the jet nozzle exit and bottom of the initial stratification. Experimental results showed that the vertical jet was strongly affected by the grating obstacle. Due to the rectifying effect, the radial spreading was suppressed and the velocity magnitude on the jet center line became larger than that in case without the grating obstacle. Meanwhile, due to the resistance effect, the integral momentum flux of the vertical jet was decayed with decrease of the aperture area ratio. It means that in case with the grating obstacle the integral jet penetration strength was decayed, although the local jet penetration to the stratification was stronger than that in case without the grating obstacle. Also, the slower stratification breakup could be observed with decrease of the aperture area ratio, indicating that stratification breakup rate to be discussed in detail considering every possible effect of a jet penetration.

論文

Experimental investigation on dependence of decontamination factor on aerosol number concentration in pool scrubbing under normal temperature and pressure

孫 昊旻; 町田 真一*; 柴本 泰照; 岡垣 百合亜; 与能本 泰介

Proceedings of 26th International Conference on Nuclear Engineering (ICONE-26) (Internet), 7 Pages, 2018/07

Pool scrubbing is one of the efficient filters with a high decontamination factor (DF). Because of its high performance, many pool scrubbing research have been performed. In the existing pool scrubbing experiments, an experimental condition of aerosol number concentration was seldom taken into account. It is probably because DF is assumed to be independent of aerosol number concentration, at least, in the concentration where aerosol coagulation is limited. The existing pool scrubbing models also follow this assumption. In order to verify this assumption, we performed a pool scrubbing experiment with different aerosol number concentrations. As a result, DF was increasing as decreasing the aerosol number concentration. In order to ensure a reliability of this result, three validation tests were performed with meticulous care. According to the results of these validation tests, it was indicated that DF dependence on the aerosol concentration was a real phenomenon of the pool scrubbing.

論文

On the liquid film flow characteristics during the rewetting in the single rod air-water system

和田 裕貴; Le, T. D.; 佐藤 聡; 柴本 泰照; 与能本 泰介

Proceedings of 26th International Conference on Nuclear Engineering (ICONE-26) (Internet), 10 Pages, 2018/07

Dry-out and rewet for an anticipated transition without scrum (ATWS) become one of the important issues. In order to predict all of these phenomena, it is necessary to cover wide range of thermal-hydraulic condition, and the modeling of precursory cooling is one of the key issues on the prediction. To reveal the precursory cooling phenomena in the rewetting process, rewetting experiment was carried out using a single heater rod in a circular glass pipe with air-water system at atmospheric pressure. Liquid film front thermal and dynamic behaviors were measured by thermocouples and visualization with a high speed camera. To establish a new rewetting model, liquid film flow characteristics including roll wave behavior, and the mass and energy balance of the liquid film at the rewetting front considering effects of sputtering were summarized in this paper.

論文

Stratification breakup by a diffuse buoyant jet; The MISTRA HM1-1 and 1-1bis experiments and their CFD analysis

安部 諭; Studer, E.*; 石垣 将宏; 柴本 泰照; 与能本 泰介

Nuclear Engineering and Design, 331, p.162 - 175, 2018/05

 被引用回数:6 パーセンタイル:20.41(Nuclear Science & Technology)

Density stratification and its breakup are important phenomena to consider in the analysis of the hydrogen distribution during a severe accident. Many previous experimental studies, using helium as mimic gas of hydrogen, focused on the stratification breakup by a vertical or horizontal jet. However, in a real containment vessel, the upward flow pattern can be considered diffuse and buoyant neither pure jet nor pure plume. HM1-1 and HM1-1bis tests in the MISTRA facility were performed to investigate such erosive flow pattern created from a horizontal hot air jet impinging on a vertical cylinder. The experimental results indicated that the jet flow was quickly mixed with the surrounding gas in the lower region of the initial stratification, and deaccelerated by buoyancy force therein. Consequently, the erosive process became slower at the upper region of the initial stratification. Those observed behavior was analyzed using the computational fluid dynamics (CFD) techniques focusing on models for turbulent Schmidt and Prndtl numbers. Some previous studies mentioned that these numbers significantly change in the stratified flow. The changes of $$Sc_{t}$$ and $$Pr_{t}$$ are very important factor to predict the stratification erosion process. The results have indicated that the simulation can be much improved by using appropriate dynamic models for those numbers. This research is a collaboration activity between CEA and JAEA.

論文

Experimental investigation of Post-BT heat transfer and rewetting phenomena

佐藤 聡; 和田 裕貴; Le, T. D.; 柴本 泰照; 与能本 泰介

Proceedings of ANS International Conference on Best Estimate Plus Uncertainties Methods (BEPU 2018) (USB Flash Drive), 12 Pages, 2018/00

本研究では、Post-BT熱伝達、液滴伝達率およびリウェット挙動を取得するため、BWRのAOOを模擬した条件において実験を行った。熱伝導方程式を解析的に解くことでリウェット挙動を調査し、リウェット速度、壁面温度および先行冷却と濡れ領域における熱伝達率の間の関係を把握した。さらに、Post-BT熱伝達とリウェット挙動へのスペーサ効果を調べるため、ATWS模擬条件において丸セル模擬スペーサを設置した実験を行った。これにより熱伝達率がモデルによる予測よりも増加すること、また低圧、高質量流束条件においてリウェット速度が増加することが示された。一連の実験を通して先行冷却が重要な役割を果たしていると考えられることから、先行冷却に着目した新しい実験を行い、リウェットフロント周辺の液膜と液滴の挙動が先行冷却メカニズムに与える影響を調べた。

論文

RANS analysis with a dynamic model for turbulent Schmidt number ($$Sc_{t}$$) on density stratification erosion in a small rectangular vessel

安部 諭; Studer, E.*; 石垣 将宏; 柴本 泰照; 与能本 泰介

Proceedings of 17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-17) (USB Flash Drive), 13 Pages, 2017/09

Density stratification and its break-up are important phenomena for discussing the containment hydrogen behavior. Turbulence transport phenomenon is one of the important factor in the stratification erosion behavior. A small scale test is a useful approach to develop a physical model for the stratification erosion because of easiness for detailed measurement. Thus, small scale experiments have been carried out in our research project named "ROSA-SA". A rectangular vessel apparatus named VIMES (VIsualization and MEasurement system on Stratification behavior) is one of such facilities, which has a vessel made of acrylic plates for visualizing flow field with the PIV measurement, whose volume is 4.05m$$^{3}$$ (1.5m(L)$$times$$1.5m(W)$$times$$1.8m(H)). In this paper, we focus on Computational Fluid Dynamics (CFD) analysis on a density stratification erosion with a vertical buoyant jet observed in the VIMES experiments. Comparative study between Large-eddy simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) are also performed to validate the dynamic turbulence Schmidt number ($$Sc_{t}$$) formulation. The results have indicated that the dynamic Sct model is advantageous to predict the observed stratification erosion behavior. This research is a collaboration activity between CEA and JAEA.

論文

Experimental study on outer surface cooling of containment vessel by using CIGMA

柴本 泰照; 石垣 将宏; 安部 諭; 与能本 泰介

Proceedings of 17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-17) (USB Flash Drive), 14 Pages, 2017/09

The present paper introduces the recent outcome from the CIGMA experiments regarding containment vessel cooling, in which an external side of a vessel upper head was flooded by water. The test vessel was initially pressurized by steam and noncondensable gas (air and/or helium), and was subsequently cooled by pouring water to the outside of the vessel top. Similar experiments were performed by authors using air-steam binary system in the previous study, which showed several characteristic phenomena such as inverse temperature stratification. The experimental conditions were extended systematically in this study to investigate the effects of initial gas composition and distribution in a vessel. The measurement results indicated that natural circulation was significantly affected by distributions of each gas species. In particular, it was enhanced when the gas density became heavier after condensation on the vessel inner wall, while it was suppressed when the gas density became lighter, creating density stratification with helium-rich gas in the upper region. The results are explained by the simplified model.

論文

Influence of mesh non-orthogonality on numerical simulation of buoyant jet flows

石垣 将宏; 安部 諭; 柴本 泰照; 与能本 泰介

Nuclear Engineering and Design, 314, p.326 - 337, 2017/04

 被引用回数:1 パーセンタイル:79.72(Nuclear Science & Technology)

本研究では浮力が支配的なジェット流れに対するメッシュの非直交性の影響を調査した。解析には三角形要素のメッシュと四角形要素のメッシュを用い、CFDコードOpenFOAMを適用した。非直交性補正を適用しない場合、三角形要素メッシュを用いて解析したジェットでは四角形要素メッシュを用いた場合よりも流れの不安定性が過大評価されることが分かった。一般に非直交補正によりメッシュの非直交性の影響は緩和されるが、計算時間が増大する。そこで、非直交補正を用いずにメッシュの非直交性の影響を緩和するための改良型ソルバを提案した。

論文

CFD simulation of a CIGMA experiment CC-PL-04 on the containment thermal hydraulics affected by the outer surface cooling

石垣 将宏; 安部 諭; 柴本 泰照; 与能本 泰介

Proceedings of 10th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-10) (USB Flash Drive), 10 Pages, 2016/11

原子力機構ではシビアアクシデント時の格納容器内熱水力挙動把握のため、大型格納容器実験装置CIGMAを製作し、実験を行っている。本発表では、蒸気及び空気の混合気体を封入した容器における外面冷却実験CC-PL-04についてCFDコードOpenFOAMにより解析した結果を報告する。

論文

Outcome of first containment cooling experiments using CIGMA

柴本 泰照; 与能本 泰介; 石垣 将宏; 安部 諭

Proceedings of 11th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, Operation and Safety (NUTHOS-11) (USB Flash Drive), 10 Pages, 2016/10

The Japan Atomic Energy Agency (JAEA) initiated the ROSA-SA project in 2013 for the purpose of studying thermal hydraulics relevant to over-temperature containment damage, hydrogen risk, and fission product transport. For this purpose, the JAEA newly constructed the Containment InteGral Measurement Apparatus (CIGMA) in 2015 for the experiments addressing containment responses, separate effects, and accident managements. Recently, we successfully conducted first experiments using CIGMA to characterize the facility under typical experimental conditions. Among these experiments, the present paper focuses on the results of containment cooling tests, for which an upper part of the vessel outer surface was cooled by spray water. Several distinctive phenomena were observed in the tests, including inverse temperature stratification in the vessel due to the cooling in the upper region. The RELAP5 analysis result was also presented to roughly indicate the prediction capability of the best-estimate two-phase flow code in predicting the containment thermal hydraulics.

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